Stuttering affects approximately 5 percent of children and can be a severe communication disorder. Family studies by the current team of speech scientists and geneticists during the past decade have provided convincing evidence that genetic factors influence the transmission of stuttering, but the identification of such genes remains elusive. We propose to localize genes influencing susceptibility to stuttering as a first step to their specific identification. Thus, we established an international collaboration, including investigators from the University of Chicago, the University of Illinois, Tel Aviv University, Israel, and Helsingborg Hospital, Sweden to enable the collection of data on the heterogeneous U.S. population, as well as more homogeneous populations from Sweden, Israel, and U. S. Hutterites. Specifically, we propose to collect data on approximately 1500 individuals from approximately 300 families (200 or more from the U. S., 50-75 from Israel and 25-50 from Sweden) and to genotype these samples for approximately 400 highly polymorphic DNA markers (10 cM map). We have already identified a large pedigree from the Hutterite genealogy, which contains 31 individuals with a history of stuttering, and a full genome scan (386 markers) has already been completed in 63 of the 127 members of this pedigree. We will conduct linkage analyses of the data from the outbred samples (U. S., Swedish, and Israeli) using multipoint parametric linkage analysis (with parameters derived from the single major locus model identified in segregation analyses of stuttering) as well as robust, allele-sharing multipoint linkage analysis. Similarly, we will conduct both parametric and robust linkage analyses in the Hutterite pedigree, as well as linkage analyses, such as homozygosity by descent mapping, and genome-wide transmission/disequilibrium tests, that are uniquely suited to the Hutterites. Preliminary studies have established the feasibility of the project, including collection and shipment of 250 blood samples (Israel, Sweden, and the U. S.), extraction of DNA, genotyping, and linkage analysis. Successful localization of genetic variation influencing susceptibility to stuttering would have enormous implications for research and treatment of stuttering, and for genetic studies of other complex disorders, especially those affecting speech and communication.